1. Field of the Invention
The present general inventive concept relates to an image forming apparatus, and more particularly, to a belt type fusing device of an improved structure to fix a developer image onto a recording medium, and an image forming apparatus having the same.
2. Description of the Related Art
Electrophotographic image forming apparatuses, such as printers, copiers, or multi-function units, generally adopt a fusing device which fixes a developer image into a recording medium with heat and pressure. Among various fusing devices, roller and belt types of fusing devices are generally used.
The main technical requirements of a fusing device include speedy warm-up and endurable fusing result. A heating source of less heat capacity is more efficient for a fast warm-up. Performance of toner fixation mainly depends on temperature, pressure, and width of nip area. In a temperature range between cold offset and hot offset, the higher temperature ensures better fixability. Also the higher pressure and wider nip area help provide better fixability.
FIG. 1 illustrates a conventional roller type fusing device. As illustrated, the conventional roller type fusing device includes a pressing roller 10 and a heating roller 20 rotating in tight contact with each other, and a heating member 30 housed inside the heating roller 20. Because the heating member 30 has high heat capacity, and the heating member 30 heats the whole area of the pressing roller 20, a warm-up takes a longer time, while a relatively narrow nip area is formed on the contact areas between the pressing roller 10 and the heating roller 20.
FIG. 2 illustrates a conventional belt type fusing device proposed to improve a warm-up speed. The fusing device includes a pressing roller 10, a fusing belt 40 to rotate with a rotational force transmitted from the pressing roller 10, a guide member 50 provided within the fusing belt 40 to guide the rotation of the fusing belt 40, and a heating member 60 formed on the guide member 50 to heat a nip area (N) created on the fusing belt 40.
Such a belt type fusing device employs the heating member 60 of a relatively low heat capacity. Also, the belt type fusing device locally heats the nip areas (N). Accordingly, the belt type fusing device has a shorter warm-up time and wider nip area (N). However, because the heating member 60 is housed at the nip areas (N) against which the pressing roller 10 is squeezed, the pressing roller 10 is required to generate a limited pressing force that the heating member 60 can endure. Because the pressing force is limited in the nip areas (N), unsuccessful fixation may occur due to lack of pressing force. However, the pressing force cannot be increased in the nip areas (N), because the heating member 60 can be damaged by the pressure and heat deformation.